This invention relates to valves in general and, in particular, to a new and useful straight flow seat valve, comprising, a valve housing, with a valve chamber, an inlet into the valve chamber, and an outlet coaxial thereto, with a seating surface for a seat body and a control cylinder in the valve chamber which is acted upon by a hydraulic or pneumatic control medium for the seat body, which can be actuated in a flow direction and is connected through a piston rod to a control piston in the control cylinder and is kept in the pressureless state of the control cylinder, on the seating surface at the outlet, by a spring acting upon the control piston.